The aims of this paper were to propose a modeling system of water UV disinfection, establish the influence of UV doses on the kinetics of disinfection, study UV-resistant strains of Pseudomonas aeruginosa, and improve the performances of this multipart process. The UV disinfection should inactivate pathogenic microorganisms and improve the hygienic quality of water. A comprehensive treatment in considering the mathematical aspect to model the UVc disinfection of water was achieved. A complete mathematical description of the inactivation kinetics is developed and showed two successive stages, a fast and a low one. Similarly, a mathematical model describing fluid flow and concentration of the microorganisms inside a UV reactor is developed. Modeling the kinetic and the UV lamp ray emission using some empirical approaches might increase the efficiency of UV disinfection and improve its performance. This study shows an improvement of the microbial inactivation rate of about 49% for the selected pathogenic resistant bacteria of P. aeruginosa (S3), and in considering perfectly mixed water flowing into the UV reactor. Key words: Disinfection, UV254, modeling, pathogenic microorganisms, performance.